The subject matter disclosed herein relates generally to a multi-modality medical imaging system. More particularly, the present disclosure relates to a system and method for defining a volume of interest on an image from a first imaging modality system based on information acquired from an image from a second imaging modality system and calculating relevant, medical parameters from the defined volume.
Single Photon Emission Computed Tomography (SPECT) imaging systems and Positron Emission Tomography (PET), referred to jointly as nuclear or NM imaging systems, generally acquire images showing physiological data based on the detection of radiation from the emission of photons. Images acquired using SPECT and/or PET are referred to as physiological images and may be used to evaluate different conditions and diseases that affect the heart or lungs, for example. Such conditions may include the size of a cancerous tumor or lesion.
SPECT and PET scans are increasingly being used in connection with other types of medical scans, including, for example, with Computed Tomography (CT) scans. CT scans generate anatomical images that are typically obtained at a much higher resolution as compared to the lower resolution physiological image from a SPECT or PET scan. The combination of the images from the scans from the two different imaging modalities, often referred to as co-registration, provides both anatomic and physiological information on a single image. Combination or multimodality imaging systems are also available to perform both scans during, the same scanning session.
Since the physiological image from the SPECT or PET scan is taken at a low resolution and the image may be noisy, it is often difficult to define the outer boundaries of the organ or lesion being examined (referred to as the target); however these boundaries are generally clearly visible in the anatomical images. As a result, the physiological images acquired from the SPECT or PET system may not include accurate volumetric measurement of the organ or lesion being examined. Additionally, anatomical structures, such as neighboring chest bones and lungs, each having different densities, may cause significant variations in the volume of the region being reviewed when using only the physiological image.
Medically relevant parameters are derived from the physiological images from the NM imaging systems. These parameters can include the total radiopharmaceutical activity in the target, the average concentration of radiopharmaceutical activity in the target, and/or the ratio of average concentration of radiopharmaceutical activity in the target to the average concentration of radiopharmaceutical activity in the surrounding tissue (referred as “background”). Inaccuracies in defining, the boundaries of the target, and “smearing” of the physiological images due to the low resolution of NM imaging system causes inaccuracies in the calculated parameters.